Air flow rate measuring device

Abstract

An air flow rate measuring device has a by-pass passage branched from a main air passage leading to an engine, and heat wires provided in the by-pass passage. The inlet of the by-pass passage is positioned at the upper end of a venturi tube disposed in the main air passage, shaped annularly, and opened to the main air passage so that the air at the inlet can be subjected to the dynamic pressure of the main air stream. The outlet of the by-pass passage also is annularly formed and opened normally to the main air stream in the main air passage. The flow rate of air sucked into the engine is measured by the heat wires subjected to air flow taken in the by-pass passage.

What is claimed is: 
     
       1. An air flow rate measuring device comprising main air passage means for introducing therethrough air into and internal combustion engine;   venturi means provided in said main air passage means for contracting an air stream to make the pressure at a portion of said main air passage means relatively lower;   by-pass passage means for by-passing a portion of said air stream of said main air passage means;   outlet means of said by-pass passage means formed at the relatively lower pressure portion of said main air passage means so that the air at said outlet means is subjected to static venturi pressure due to the air stream flowing in said main air passsage means;   inlet means of said by-pass passage means disposed upstream of said outlet means and formed as an annular slit along the inner circumference of said main air passage means, a downstream side of a slit defining surface of said inlet means projecting slightly into said main air passage means such that the inlet means is opened to said main air passage means in radial and axial directions so that the air at said inlet means is subjected to the dynamic pressure due to the air stream flowing in said main air passage means; and   sensor means disposed in said by-pass passage means for measuring the flow rate of air flowing in said by-pass passage means.   
     
     
       2. The device as defined in claim 1, wherein said venturi means comprise a venturi tube, and said inlet means is defined at the end of said venturi tube disposed upstream of said outlet means. 
     
     
       3. An air flow rate measuring device comprising main air passage means for introducing therethrough air into an internal combustion engine;   venturi means provided in said main air passage means for contracting an air stream to make the pressure at a portion of said main air passage means relatively lower;   by-pass passage means for by-passing a portion of said main air passage means;   outlet means of said by-pass passage means formed at the relatively lower pressure portion of said main air passage means;   inlet means of said by-pass passage means disposed upstream of said outlet means and formed angularly along the inner circumference of said main air passage means, said inlet means projecting slightly into said main air passage means and being open in radial and axial directions to said main air passage means so that the air at said inlet means is subjected to the dynamic pressure due to the air stream flowing in said main air passage means; and   sensor means disposed in said by-pass passage means for measuring the flow rate of air flowing in said by-pass passage means, wherein said outlet means of said by-pass passage means is formed annular and opened normally to the main air stream.   
     
     
       4. An air flow rate measuring device comprising a suction tube for introducing air into an internal combustion engine, said suction tube having a throat portion which forms an inner shoulder inside said suction tube;   a venturi tube disposed in said suction tube so that the lower end of said venturi tube rests on said inner shoulder;   a cylinder disposed inside said suction tube so as to rest on the upper end of said venturi tube;   a by-pass passage by passing said venturi tube, an inlet of said by-pass passage being defined by the lower end of said cylinder and the upper end of said venturi tube so as to project inside the inner face of said cylinder;   an outlet of said by-pass passage being defined by the lower end of said venturi tube and said inner shoulder of said suction pipe; and   means including a hot wire disposed in said by-pass passage for measuring the flow rate of air flowing in said by-pass passage.   
     
     
       5. The device as defined in claim 4, wherein the outside of said venturi tube is so tapered at both end portions that the diameter will reduce toward both ends thereof, and the tapered portions each form a part of said by-pass passage whereby the air flow in said by-pass passage is stable and the by-pass ratio of the air is increased. 
     
     
       6. The device defined in claim 4, wherein the diameter of said venturi tube at the outer top end is less than that of the inner diameter of said cylinder so that said inlet of said by-pass passage is opened against the air stream in said cylinder. 
     
     
       7. The device defined in claim 6, wherein said outlet of said by-pass passage is opened normal to the air stream. 
     
     
       8. The device as defined in claim 4, wherein the inlet of said by-pass passage forms an annular slit which opens at an angle to the main air passage through said suction tube and the upper end of said venturi tube is slightly projected into said main air passage with respect to said cylinder so that the air disposed at said slit will be subjected to the dynamic pressure of the air flowing through said main air passage. 
     
     
       9. The device defined in claim 8, wherein said outlet of said by-pass passage is opened normal to the air stream. 
     
     
       10. An air flow rate measuring device for an internal combustion engine, comprising: main air passage means for introducing therethrough air into an internal combustion engine and having a relatively lower pressure portion at which the air stream is at a lower pressure than other portions thereof;   by-pass passage means for by-passing a portion of said air stream of said main air passage means, including outlet means communicating with the air stream at said relatively-lower pressure portion of said main air passage means so that the air at said outlet means is subjected to the static pressure of the air stream flowing in the main air passage means at this point, and inlet means disposed upstream of said outlet means and formed as an annular slit along the inner circumference of said main air passage means, a downstream of a slit defining surface projects slightly into said main air passage means such that the inlet means is open in radial and axial directions so that the air at said inlet means is subjected to the dynamic pressure due to the air stream flowing in said main air passage means; and   sensor means disposed in said by-pass passage means for measuring the flow rate of air flowing in said by-pass passage means.   
     
     
       11. The device as defined in claim 10, wherein said outlet means of said by-pass passage means is formed annular and opened normally to the main air stream. 
     
     
       12. The device as defined in claim 10, wherein the portion of said by-pass passage means disposed between said inlet means and said outlet means thereof is of non-annular configuration. 
     
     
       13. The device as defined in claim 12, wherein said non-annular portion of said by-pass passage means is non-coaxially arranged with respect to said main air passage means. 
     
     
       14. The device as defined in claim 10, wherein said slit defining surface extends at an angle to the axis of said main air passage means so that the air disposed at said slit will be subjected to the dynamic pressure of the air flowing through said main air passage.